Those held are not directly linked to the attack or even suspected of knowing who might be, but were rounded up on other charges, like failing to provide identification or registration documents, possession of weapons, and then resisting arrest. According to the Russian news agency Itar-Nass, officials targeted migrants from ex-Soviet states and the Caucuses, where Islamist extremists have vowed to develop an Islamic state. (And where the actual attackers are most likely to have come from.) Residents of the Caucuses have long-complained of unjust treatment from the government in Moscow and these latest incidents certainly won't lower the tension in the region.

No group has yet claimed responsibility for the attacks, but Islamist militants, instructed by a Chechen leader back in July to use "maximum force" to block the Sochi Winter Olympic Games, are the main suspects. According to Reuters, police are seeking out a male in relation to Monday's blast:

Investigators said they believed a male suicide bomber was responsible for Monday's morning rush-hour blast, which turned a trolleybus into a twisted wreck and left bodies lying in the street... In Sunday's attack, authorities initially described the bomber as a woman from Dagestan, but later said the bomber may have been a man.

The controversial choice for Winter Olympics host has shined a light on Russia's poor human rights record and regressive attitude towards LGBT citizens and prompted various reforms critics call superficial, are slated to begin on February 7 and last through February 23.

News reports are focusing on the Germanwings pilot's possible depression, following a familiar script in the wake of mass killings. But the evidence shows violence is extremely rare among the mentally ill.